1. Field of the Invvention
This invention relates to a method for constructing underpass, particularly the underpass across railway and highway, without affecting the normal trafffic thereof.
2. Description of the Prior Art
Conventionally, methods adopted for constructing underpass across railway and highway include the "tunnel digging" method and the "thrust propelling" method.
The "tunnel digging" method is a primitive process commonly adopted in the construction of underpasses. Although it requires less power equipment, yet much working time and manpower are needed in the process of construction because a good deal of protective works such as steel pipe roof and support ground have to be built before starting the digging operation. In addition, excavation of the earth work and building of the buttress support and concrete top frame have to be done alternatively. Moreover, in the process of excavation, security problem is a main concern as this method is subject to the vibration caused by the traffic on the road surface, often resulting in the sagging of the road foundation.
In the "thrust propelling" method, protective works such as steel pipe roof and piled wall have to be arranged, and a strong reaction wall has to be built for thrust propelling operation. Besides, heavy-duty power facilities such as pushing and pulling jacks have to be used for thrusting the precast box culvert into the road foundation in conjunction with the construction line. Such method also suffers because it requires more manpower, more working time, and more costs. Moreover, if any error occurs in the process of thrusting, it is very difficult to make correction therefrom.